This invention relates generally to fluid pumps and more specifically to a pneumatic underground fluid recovery device for use in a well to pump underground fluids therefrom.
Increasing public awareness and concern over the widespread contamination of the world's aquifers has caused legislation to be promulgated mandating reduced contamination levels of ground water. The range of contaminants regulated include gasoline, diesel, and fuel oils as well as coal tar, creosote and a multitude of other organic and inorganic compounds. Additionally, landfill leachates have been regulated to prevent the contamination of surrounding aquifers.
As a result, various pumping systems have been developed in an attempt to remove hazardous chemicals and the like from groundwater. Typically, the central component of these systems includes an underground pump installed in a remediation well approximately at the water table for extracting either the free-phase floating or sinking contaminants, the contaminated groundwater, or some combination thereof from the well. The underground pump is either pneumatically or electrically powered depending on the particular installation. For example, electrically powered pumps are more efficient and more economical to operate than pneumatic pumps in large multiple pump installations, while pneumatic pumps generally require less safety equipment and associated expense for installations having potentially explosive vapors and gases. Pneumatic pumps offer the additional advantage of pumping underground fluids with a minimum of turbulence and mixing. As a result, subsequent gravity separation is more simply accomplished over that associated with electrically powered pumps, which tend to break free-phase hydrocarbons into extremely small droplets and/or emulsify the pumped underground fluid.
Regardless of the type of power chosen, the pump must further withstand the wet and typically corrosive environment encountered in and around remediation wells. For example, in prior known pneumatic pump systems, such as those disclosed in U.S. Pat. Nos. 4,527,633, 4,489,779, 4,826,406 and 5,027,902 to McLaughlin et. al, liquid is admitted to the pump vessel through a static pressure responsive check valve which is prone to fouling or otherwise clogging from biological growths and mineral deposits, thereby degrading the performance of, or even worse, disabling the pump. This is especially true for top filling pumps in which only the force of the head of liquid above the pump, in many instances less than one inch of water column, is available to unseat the flapper sealing element of the check valve. Further aggravating this problem is the small porting required of the top filling static pressure responsive check valve so that the valve opens or "cracks" at the low pressures. Inlet screens have been employed in an attempt to reduce the fouling; however, these too have been found to quickly clog from biological growths and mineral deposits, thereby disabling the pump. Therefore, a need exists for an underground fluid recovery device that is less susceptible to fouling.
Preferably, the pump should be able to compensate and adjust for static fluid level variations in the remediation well. For example, to skim free-phase floating or sinking contaminants from an aquifer, the pump is desirably positioned so that its inlet is located very near the contaminant/water interface. Unfortunately, static well level rarely remains constant for very long periods of time due to the effects of rain, tides, pumping from nearby wells and/or other hydrogeologic events. Static well level changes of only a few inches can render a pump ineffective.
In U.S. Pat. No. 4,678,040 to McLaughlin, the pump compensates for static fluid level variations in the well by adjusting the inlet of the pump relative to the pump via an external float. However, the size of the float is limited by the diameter of the remediation well. For remediation wells four inches in diameter or less, a small float must be used, limiting the available buoyancy force to only a few ounces and a range of travel less than two feet. Even under optimal conditions, this range of travel is not adequate for many installation sites, especially those, for example, near coastlines where tidal fluctuations alone may be three feet or more. Further, similar to the static pressure responsive inlet valve, the external float is susceptible to the accumulation of biological and mineral deposits that change the specific gravity of the float, increase the stiffness of the coiled tube connecting the float to the collection vessel and/or close off the clearance area between the float and its guide rod--all of which, alone or in combination, can quickly disable the float and render the pump ineffective. Therefore, a need exists for an underground fluid recovery device that compensates for static fluid level variations in the well while being resistant to fouling.
Other devices, for example U.S. Pat. No. 4,826,406 to Wells, maintain the pump near the contaminant/groundwater interface; however, the groundwater is pumped along with the contaminant. Because of regulations governing the storage and disposal of groundwater pumped from a remediation well, it is desirable to pump only the contaminants from the well. Therefore, a need exists for an underground fluid recovery device which compensates for static fluid level variations in the well while maintaining the inlet of the pump near the surface of the contaminant/groundwater interface. In Wells, the remediation well fluid level is not sensed, therefore requiring the pump to be fully retracted before the beginning of every pump cycle and resulting in long cycle times and limited recovery rates. A need further exists for an underground fluid recovery device that senses fluid level within the remediation well.
In addition to the pump sensing fluid level in the well, it is also desirable that the pump be automatically self-optimizing; i.e., the pump automatically responding to changing system parameters such as fill head, discharge head and compressed air supply pressure. For example, in the pneumatic pumps disclosed in U.S. Pat. Nos. 4,527,633, 4,489,799, 4,826,406 and 5,027,902 to McLaughlin et. al, the fill and empty cycles are of a fixed duration preprogrammed in an open loop pneumatic or electric timer. In order to maximize pumping rates, an iterative process is required to achieve optimal pump performance, typically requiring that the timers be set by trained personnel familiar with the pump's design and function. However, the optimal fill and empty timed cycles are dependent upon system parameters which change over time to detract from optimal performance of the pump. For example, although the pump fill and empty timed cycles may be initially optimized when the pump is installed submerged in five or ten feet of water, these preprogrammed cycles do not provide optimal pump performance after the well is brought down by several feet. If the fill cycle is not adjusted to reflect the decreased head (increased fill time), the pump vessel will not fill completely during the preprogrammed fill cycle. A need therefore exists for an underground fluid recovery device that automatically adjusts to changing system parameters to maintain optimal pump performance. Preferably, in a pneumatic control circuit, all controls associated with the aforementioned pump would be located down well adjacent to or integral with the pump to minimize time lags.
Similarly, if the empty cycle is set too long or becomes too long due to changing system parameters, pump performance will deteriorate. Further, compressed air will be blown up the discharge line, creating two-phase flow which can damage downstream centrifugal pumps, valves and flowmeters and aggravating the build-up of mineral scale deposits, especially in landfill leachate pumping applications. A need therefore exists for an underground fluid recovery device that prevents compressed air from being blown up the discharge line following the empty cycle for a pneumatic pump.